The present invention relates to an angle detection apparatus and a torque detection apparatus.
Japanese Laid-Open Patent Publication No. 5-264292 discloses an angle detection apparatus equipped with a resolver. A resolver is a rotary transformer, in which the magnetic relationship between a primary coil (excitation section) and a secondary coil (a sensor coil of an output section) changes. In the sensor coil of the output section, an output signal (voltage) is evoked that has an amplitude proportionate to the amplitude of an excitation signal inputted to the primary coil. The output signal is a function on a sine wave and very accurately represents a rotation angle.
A resolver type angle detection apparatus is an absolute angle detector that detects absolute rotation angles of a rotary shaft in a single rotation, or an absolute angle, based on output signal of the resolver. A resolver type angle detection apparatus can perform highly accurate detection through multi-polarization, and is characterized by its high durability and noise resistance because of the simple structure.
However, in the actual use environment of a resolver type angle detection apparatus, not only absolute angles of a rotary shaft in a single rotation, but also absolute angles in multiple rotations, or multiple rotation absolute angles need to be detected. For example, in a case of the steering apparatus of a vehicle, an absolute angle that corresponds to a turning angle of the steering wheel and is greater than or equal to a single rotation of the steering shaft (360°) needs to be detected.
However, since an output signal of a resolver corresponds to a turn within a single rotation of a rotary shaft as described above, a resolver type angle detection apparatus having an ordinary configuration cannot detect multiple rotation absolute angles of a rotary shaft. Thus, a plurality of resolvers need to be coupled to one another with gears when using resolvers for detecting multiple rotation absolute angle. As a result, the size and costs of the angle detection apparatus are increased.
In this respect, in a conventional vehicle steering apparatus, a resolver as described above is used together with an incremental detector that accumulates increase and decrease in the displacement amount of a rotary shaft, so that multiple rotation absolute angles are computed.
However, an incremental detector is generally susceptible to noise. Therefore, when accumulating displacement amount, the accumulated value of displacement amount might be significantly different from the actual value because of the influence of, for example, noise. Also, although a resolver basically has a superior noise resistance and durability, abnormalities such as broken wires and short circuits in coils may occur in the resolver. If such an abnormality occurs, the resolver cannot accurately detect multiple rotation absolute angles.